Indicating instrument

ABSTRACT

The invention relates to an indicating instrument, in particular for a motor vehicle, having a housing with a front frame holding a cover pane, and an elastic spacing element arranged between the cover pane and front frame, and to a method for connecting the cover pane to the front frame.  
     In order to ensure a reliable connection between the cover pane and front frame which is without play, the invention proposes the spacing element be placed in an axial cutout which is arranged in the region of the circumference of the front frame and faces the cover pane, and in which the cover pane can engage. The method consists in that in a first step the spacing element is inserted into the axial cutout in the front frame, and in a second step the cover pane is pressed into the axial cutout against the spacing element.

[0001] The invention relates to an indicating instrument, in particularfor a motor vehicle, having a housing with a front frame holding a coverpane, and an elastic spacing element arranged between the cover pane andfront frame. The invention also relates to a method for connecting acover plate to a front frame of such an indicating instrument.

[0002] Such an indicating instrument is known, a cover pane engaging ina radial cutout, forming an axial recess, in an instrument housing, andin this case bracing a sealing ring likewise arranged in the radialcutout. The cover pane must be cambered for mounting, and a specialmounting tool is required for inserting the pane into the housing. Thisassembly is expensive and complicated, as a result of which it isvirtually impossible to automate the production. Moreover, the choice ofmaterial for the cover pane is fixed to the greatest possible extent,since the latter must have at least slight intrinsic elasticity, andthere is the risk of damaging the pane during installation.

[0003] Moreover, indicating instruments are known in which the coverglasses are each welded to the front frame. This is an expensiveproduction method which, in addition, can be applied only to a few pairsof materials. It is also known for the cover pane and front frame to beclipped. These clip connections are affected by play as a result ofwhich noise is continuously developed in the event of flexing of theindicating instrument such as occurs regularly, in particular in motorvehicles, through persistent vibrational excitation. Moreover, in thecase of these connections dust penetrates into the indicatinginstrument, as a result of which both the legibility of the instrumentcan be worsened and its operating reliability is reduced.

[0004] It is therefore the object of the invention to create anindicating instrument of the type mentioned at the beginning which onthe one hand at least largely excludes penetration of pollutants intothe instrument, and on the other hand ensures a permanent connection,without play, between the cover pane and front frame. Moreover, it is tobe possible to produce the indicating instrument in a particularlysimple and cost-effective fashion in large batch numbers. Moreover, theaim is to develop a method for simplified connection of a cover pane toa front frame of such an indicating instrument.

[0005] The first-named object is achieved according to the invention byvirtue of the fact that the spacing element is placed in an axial cutoutwhich is arranged in the region of the circumference of the front frameand faces the cover pane, and in which the cover pane can engage. Such adesign ensures that the cover pane bears securely against the frontframe without a relative movement of the components with respect to oneanother, for example excited by external vibrations, causing theelements to slide on one another, thus excluding undesired noisedevelopment. Moreover, it is possible in a simple way with the aid ofthe indicating instrument according to the invention to even out betweenthe cover pane and front frame manufacturing tolerances which can reacha substantial dimension, particularly in the case of large-areaindicating instruments. In addition, together with the axial cutout thespacing element permits optical concealment of the connecting regionbetween the cover pane and front frame; it is possible to eliminate anadditional cover for this, and the complete circumference of theindicating instrument can be directly visible to a viewer in a fashionwhich reduces the installation space of the indicating instrument.Because the cover pane can engage in the axial cutout, the indicatinginstrument according to the invention is particularly simple to mount,since the cover pane can be directly connected to the front frame fromthe front without being tilted or cambered.

[0006] It is conceivable that the axial cutout is arranged only insections in the region of the circumference of the front frame. However,a particularly tight and homogenous connection between the cover paneand front frame is permitted when, in accordance with an advantageousdevelopment of the invention, the axial cutout in the region of thecircumference of the front frame runs continuously around the latter. Asa result, the operation of joining the cover pane and front frame isalso simplified at the same time.

[0007] In accordance with another advantageous development of theinvention, the axial cutout has a groove-shaped cross section such thaton the one hand an exact position of the cover pane with respect to thefront frame is ensured, and on the other hand the groove base can forman axial stop in a simple way when the cover pane and front frame arejoined. Both the joining operation and the insertion of the spacingelement into the axial cutout are advantageously substantiallysimplified when the groove has flanks diverging toward the cover pane.

[0008] A particularly reliable fixing of the spacing element on thefront frame can be achieved when, in accordance with anotheradvantageous development of the invention, the groove base of the axialcutout has an indentation pointing away from the cover pane, in whichthe spacing element can be held.

[0009] It would be possible, for example, to imagine that the spacingelement is a rubber element and can be laid in the axial cutout in thefront frame. By contrast, the spacing element can be arranged in aparticularly simple way on the front frame when it advantageouslyconsists of a hard-setting material. In addition, adaptation to the partof the cover pane engaging in the axial cutout can be performed in thiscase during hardening.

[0010] In accordance with another advantageous development of theinvention, a particularly simple and reliable connection between thecover pane and front frame is achieved when the spacing element has anadhesive. The spacing element thus simultaneously fulfills the functionsof sealing the instrument, connecting the cover pane to the front frameand mechanically decoupling and damping these components.

[0011] It is basically the case that the most varied materials, whichadvantageously simplify the processing and installation of the spacingelement, for example thermoplastic elastomers, are suitable for thespacing element. However, it is particularly advantageous when thespacing element preferably consists of a polymer foam. This materialflows easily even under a slight pressure in the case of conventionalprocessing temperatures, and sets hard without volatile byproducts.Moreover, virtually no shrinkage occurs during the hard-setting, withthe result that the spacing element is dimensionally correct and notprone to stress cracking.

[0012] In accordance with another advantageous development of theinvention, the spacing element can be clamped between the front frameand cover pane so that, as a result of the clamping force, it ensures asealing connection and reliable decoupling of the front frame and coverpane over the entire service life of the indicating instrument.

[0013] It is conceivable for the front frame and the cover pane to bescrewed together or merely interconnected by means of an adhesive. Theindicating instrument is, by contrast, particularly durable even undervibrating stress such as occurs in motor vehicles, and it can also bemounted very simply when the front frame and the cover pane canadvantageously be interconnected by means of a clip device. In thiscase, a particularly reliable connection is ensured when arranged at amutual spacing in the region of the circumference of the cover pane areat least two clips which can engage in corresponding clip lugs arrangedon the front frame. A particularly high pressure can advantageously beexerted on the spacing element when the clip device is arranged in theregion of the spacing element. In order in this case to maintain thefull functionality of the spacing element, it is particularlyadvantageous when, in accordance with another development of theinvention, the spacing element has indentations or cutouts through whichthe clips can engage.

[0014] In accordance with another advantageous development of theinvention, in the region of its circumference the cover pane has a webpointing to the front frame approximately in the axial direction of theindicating instrument. This web can be arranged in sections, but it isespecially advantageous for a particularly tight connection between thecover pane and front frame if the web runs continuously around the coverpane in the region of its circumference. The web could, for example,serve merely as a joining aid. However, it is particularly advantageousif the web can be put against the spacing element, and can thussimultaneously support the connection between the cover pane and frontframe and exert a clamping force on the spacing element. Thetransitional, and thus damping and sealing surface between the coverpane and front frame is particularly large if, in accordance withanother advantageous development of the invention, the web can engage inthe spacing element.

[0015] Because of the simple assembly, rendered possible by theinvention, of the cover pane and front frame by axially joining thesetwo components and decoupling them fully mechanically, as a result ofwhich their connection can be maintained in simple, stress-free fashion,a very wide range of materials can be used for the cover pane and thefront frame. However, because of good optical properties, which are tobe seen in a high degree of transparency and an excellent surfacequality, it is particularly advantageous if the cover pane consists of amaterial having polymethyl methacrylate (PMMA). This excludes thepossibility of poor optical quality of the cover pane, and thusdefective legibility of the indicating instrument, posing a risk totraffic safety. The front frame can be produced in a particularly simpleand cost-effective fashion when it preferably consists of a materialhaving polypropylene (PP).

[0016] The second-named object, specifically creating a method forsimplified connection between a cover pane and a front frame of anindicating instrument according to the invention, is achieved accordingto the invention by virtue of the fact that in a first step the spacingelement is inserted into the axial cutout in the front frame, and in asecond step the cover pane is pressed into the axial cutout against thespacing element. This method advantageously requires no manualdexterity; it easily renders possible a high degree of automation inproduction, it being possible at the same time to produce very highbatch numbers per unit of time. The spacing element can be positionedwith precision in a very simple way according to the insertion of thespacing element into the axial cutout. Pressing the cover pane into theaxial cutout constitutes a simple joining operation on one axis.

[0017] The spacing element preferably consists of a material which flowswhen being inserted into the axial cutout, and is injected into theaxial cutout. Thus, it is possible in a particularly simple way toinsert the spacing element into the axial cutout with the aid of aninjection nozzle, which can easily be positioned opposite the axialcutout, without an additional joining operation. It would be conceivablefor the spacing element to remain in a viscose state after the insertionof the cover pane. However, a particularly firm and lasting connectionbetween the cover pane and front frame results when the spacing elementadvantageously sets hard after the assembly of the front frame and coverpane.

[0018] For example, a bonded connection is adequate enough for holdingthe cover pane on the front frame. In accordance with anotherdevelopment of the invention, however, it is particularly advantageousif the front frame and the cover pane are clipped to one another. Owingto the clipped connection, it is additionally possible permanently toexercise a clamping force on the spacing element, with the result thatit can position the front frame and cover pane relative to one anotherwith prestressing.

[0019] The invention can be carried out in very different ways. It isexplained in more detail below with the aid of exemplary embodimentsrepresented in the attached drawings, in which:

[0020]FIG. 1 shows an indicating instrument in an explodedrepresentation,

[0021]FIGS. 2, 3 show a section of a front frame and of a cover pane ina first embodiment, and

[0022]FIGS. 4, 5 show a section of front frame and a cover pane in asecond embodiment.

[0023] Represented before mounting in FIG. 1 is an indicating instrumentaccording to the invention having a front frame 2, a printed circuitboard 9 and a rear wall 10. A cover pane 1 can be clipped on the frontside of the front frame 2. A plurality of measuring elements 11, pilotlamps 19 and incandescent lamps 20 are arranged on the printed circuitboard 9. The measuring elements 11 serve to drive pointers 12 which, inthe mounted state of the indicating instrument, can pivot over a dial 6.The dial 6 is made from a translucent material and provided forfastening on a printed circuit board 8 which can be illuminated by theincandescent lamps 20. Together with the pointers 12 and the dial 6, themeasuring elements 11 respectively form an indicating unit which whencombined with further indicating units form the indicating instrumentalso denoted as a instrument cluster. Such instrument clusters arepreferably used in motor vehicles and are usually installed there in thedashboard.

[0024] The front frame 2 has a plurality of cutouts 13 for theindicating units, and is constructed in one piece with light shafts 15for the pilot lights 19. The front side of the front frame 2 serves forfastening a cover 7. In a fashion corresponding to the cutouts 13 of thefront frame 2, this cover 7 has cutouts 14 for the indicating units, andcovers the light shafts 15 in the mounted state. Furthermore, the frontframe 2 has a plurality of holding parts 17 for fastening the instrumentcluster in the dashboard of the motor vehicle. The instrument cluster isconnected electrically to the vehicle electronics by means of plug-incontacts arranged on the printed circuit board 9.

[0025] The dial 6 and the printed circuit board 8 in each case have acutout 22 for a flat display screen 26 to be arranged on the printedcircuit board 9. An incandescent lamp 21 is provided on the printedcircuit board 9 for the purpose of illuminating the flat display screen26. The optical conductor plate 8 has a further cutout 16, through whichadditional information can be represented on the dial 6 by a series oflight-emitting diodes 18 arranged on the printed circuit board 9. Lightshafts 35 required for this purpose are provided for mounting on theprinted circuit board 9. One cutout 25 present in the front frame 2 andthe cover frame 1 serves the purpose of guiding through an operatingelement 23 for resetting a trip meter.

[0026] The previously described individual parts of the indicatinginstrument are assembled essentially in the axial direction B of theindicating instrument. In order to connect the cover pane 1 to the frontframe 2, in the region of its circumference 32 the cover pane 1 hasclips 29, and in the region of its circumference 27 the front frame 2has clip lugs 30 corresponding to the clips 29. The clips 29 can engagein the clip lugs 30.

[0027] In order to explain the connection of the front frame 2 and thecover pane 1, a section of the edge region of a front frame 2 and acover pane 1 is represented enlarged in FIGS. 2, 3 in an alternativeembodiment, a plane 5 in which a dial is to be arranged, and a cutout 13in the front frame 2 for an indicating unit being illustrated for thepurpose of explaining the position of the section. FIG. 2 shows the twocomponents before they are assembled in the illustrated joiningdirection A, which corresponds approximately to the axial direction B ofthe indicating instrument (FIG. 1). FIG. 3 shows the assembled state. Itis to be seen that an axial cutout 4 facing the cover pane 1 is arrangedin the region of the circumference 27 of the front frame 2. An elasticspacing element 3 having an approximately U-shaped cross section isinserted into this axial cutout 4, running continuously around the frontframe 2 in the region of the circumference 27 thereof. The axial cutout4 is constructed in this case in the shape of a groove, and the spacingelement 3 bears directly against its groove base 33 and the grooveflanks 24, 36. A web 28 running around the circumference of the coverpane 1 can engage in the spacing element 3.

[0028] A similar section of a circumferential region of a front frame 2and a cover pane 1 is shown in FIGS. 4, 5 in an embodiment correspondingto FIG. 1. Here, as well, a dial plane 5 is illustrated for the purposeof explaining the position of the section. Arranged in the region of thecircumference 27 of the front frame 2 is a groove-shaped axial cutout 4running around continuously. Injected, as spacing element 3, into theaxial cutout 4, whose groove base 33 has an indentation 34 pointing awayfrom the cover pane 1 is a polyester foam which sets hard after theinjection operation and remains in an elastic state. Clip lugs 30arranged on the circumference 27 of the front frame 2 hold clips 29correspondingly fitted on the circumference of the cover pane 1.Pressing onto the spacing element 3, which has set hard, in theassembled state is a web 28 of the cover pane 1 which braces the spacingelement 3 against the groove base 33 and the indentation 34 in the axialcutout 4 after latching in the joining direction A of the clip device 31comprising the clip 29 and clip lug 30.

1. An indicating instrument, in particular for a motor vehicle, having ahousing with a front frame holding a cover pane, and an elastic spacingelement arranged between the cover pane and front frame, wherein thespacing element (3) is placed in an axial cutout (4) which is arrangedin the region of the circumference (27) of the front frame (2) and facesthe cover pane (1), and in which the cover pane (1) can engage.
 2. Theindicating instrument as claimed in claim 1, wherein the axial cutout(4) in the region of the circumference (27) of the front frame (2) runscontinuously around the latter.
 3. The indicating instrument as claimedin claim 1 or 2, wherein the axial cutout (4) has a groove-shaped crosssection.
 4. The indicating instrument as claimed in claim 3, wherein thegroove base (33) of the axial cutout (4) has an indentation (34)pointing away from the cover pane (1).
 5. The indicating instrument asclaimed in one of the preceding claims, wherein the spacing element (3)consists of a hard-setting material.
 6. The indicating instrument asclaimed in one of the preceding claims, wherein the spacing element (3)has an adhesive.
 7. The indicating instrument as claimed in one of thepreceding claims, wherein the spacing element (3) consists of apolyester foam.
 8. The indicating instrument as claimed in one of thepreceding claims, wherein the spacing element (3) can be clamped betweenthe front frame (2) and cover pane (1).
 9. The indicating instrument asclaimed in one of the preceding claims, wherein the front frame (2) andthe cover pane (3) can be interconnected by means of a clip device (31).10. The indicating device as claimed in claim 9, wherein arranged at amutual spacing in the region of the circumference (32) of the cover pane(1) are at least two clips (29) which can engage in corresponding cliplugs (30) arranged on the front frame (2).
 11. The indicating instrumentas claimed in claim 10, wherein the spacing element (3) has indentationsor cutouts through which the clips (29) can engage.
 12. The indicatinginstrument as claimed in one of the preceding claims, wherein in theregion of its circumference (32) the cover pane (1) has a web (28)pointing to the front frame (2) approximately in the axial direction (B)of the indicating instrument.
 13. The indicating instrument as claimedin claim 12, wherein the web (28) can be put against the spacing element(3).
 14. The indicating instrument as claimed in claim 13, wherein theweb (28) can engage in the spacing element (3).
 15. The indicatinginstrument as claimed in one of the preceding claims, wherein the frontframe (2) consists of a material having polypropylene (PP), and thecover pane (1) consists of a material having polymethyl methacrylate(PMMA).
 16. A method for connecting a cover pane to a front frame of anindicating instrument according to one of the preceding claims, whereinin a first step the spacing element (3) is inserted into the axialcutout (4) in the front frame (2), and in a second step the cover pane(1) is pressed into the axial cutout (4) against the spacing element(3).
 17. The method as claimed in claim 16, wherein the spacing element(3) consists of a material which flows when being inserted into theaxial cutout (4), and is injected into the axial cutout (4).
 18. Themethod as claimed in one of claims 16 or 17, wherein the spacing element(3) sets hard after the assembly of the front frame (2) and cover pane(1).
 19. The method as claimed in one of claims 16 to 18, wherein thefront frame (2) and the cover pane (1) are clipped to one another.